$ perl -MEncode -Mcharnames=:full -wE'
   $bad = "\xE9abc";
   say sprintf "U+%04X %s", ord, charnames::viacode(ord)
      for split //, decode("UTF-8", $bad);
'
U+FFFD REPLACEMENT CHARACTER
U+0061 LATIN SMALL LETTER A
U+0062 LATIN SMALL LETTER B
U+0063 LATIN SMALL LETTER C